It is common in the art to utilize an antenna array comprised of a plurality of antenna elements in order to illuminate a selected area with a signal or signals. Often such an array is used in combination with beam forming techniques, such as phase shifting the signal associated with particular antenna elements of the array, such that the signals from the excited elements combine to form a desired beam, or radiation pattern, having a predetermined shape and/or direction.
For example beam forming matrices coupled to an antenna array, such as a phased array panel antenna, have been used in providing multiple antenna beams. One such solution utilizes a four by four Butler or hybrid matrix, having four inputs to accept radio frequency signals and four outputs each of which is coupled to an antenna element or column of elements of a panel phase array antenna, to provide four antenna beams, such as four 30.degree. directional antenna beams. Each of the antenna beams of the above phased array is associated with a particular input of the beam forming matrix such that a signal appearing at a first input of the beam forming matrix will radiate in a first antenna beam by the input signal being provided to each of the four antenna elements coupled to the outputs of the beam forming matrix as signal components having a proper phase and/or power relation to one another. Likewise, a signal appearing at a second input of the beam forming matrix will radiate in a second antenna beam by the input signal being provided to each of the four antenna elements as signal components having a proper phase and/or power relation to one another which is different than the phase and/or power relation as between the signal components of the first beam. Accordingly, the beam forming matrix provides a spatial transform of the signal provided at a single input of the beam forming matrix.
Therefore, it is often desirable to provide signal input paths sufficient in number to result in the controllable excitation of the antenna columns as described above. For example, where twelve antenna beams are to be utilized, such as by deploying three four beam antenna arrays as described above in near proximity to result in 360.degree. radiation of antenna beams, twelve signal input paths, each associated with a particular antenna beam, may be utilized.
In order to provide a signal of sufficient amplitude it is often desirable to provide amplification in each of the signals communicated. One method of providing such signal amplification uses a back to back hybrid matrix combination having sixteen linear power amplifiers (LPAs) disposed between a hybrid matrix and an inverse hybrid matrix to provide a distributed or load sharing amplifier suite, wherein the four inputs and outputs that do not correspond to an antenna beam are terminated. The advantage of this arrangement is that a hybrid matrix takes a signal input at any of the matrix's inputs and effectively provides a Fourier transform of the signal. This results in an input signal, provided to an input of the input hybrid matrix, appearing at each of the matrix's outputs as a linear phase progression (i.e., the input signal is dissected into components each appearing at a different hybrid matrix output). By amplifying each of these component signals, and applying the result to an inverse hybrid matrix, an amplified version of the original signal, including all of its components, may be had.
In order to transmit signals on a single beam of the four beam array using the beam forming network described above, the signal must be incident on only one of the four input ports of the beam forming network. This implies that the signals are transmitted out of one port of the above load sharing amplifier suite. However, in order to transmit the signal in any pattern other than the single beam from the beam forming matrix described above, i.e., beam syntheses, more than one input of the beam forming matrix must be driven. This implies that there are coherent signals present on more than one output of the load sharing amplifier suite and, accordingly, certain input ports of the load sharing amplifier inverse matrix must have complex vector summation.
Such complex vector summation at the input of the load sharing output matrix assures that the amplifiers driving the input ports of the load sharing output (inverse) matrix will contribute power unevenly to the antenna pattern which is generated. Generally, the greater the number of input ports of the beam forming matrix that are driven, the greater the degree of imbalance between amplifiers in the load sharing amplifier suite. Accordingly, the load is no longer distributed among the amplifiers of the load sharing amplifier suite when the system is utilized to radiate signals in patterns other than the single antenna beams defined by the beam forming matrix.
Signals, such as CDMA signals or signaling channels, may be provided in radiation patterns co-extensive with multiple ones of the antenna beams of such a system, such as when an omni directional beam is synthesized, requiring the driving of multiple, if not all, inputs of the beam forming matrix. This creates the worst possible power distribution among the amplifiers in the load sharing amplifier suite, as the above problems with unequal distribution of the signal across the amplifiers of the load sharing amplifier suite are experienced.
Moreover, CDMA signals have a high peak to average power ratio, causing such signals to be very demanding of linear power amplifier hardware for peak power handling. When multiple CDMA signals are transmitted through an amplifier, the problem is compounded due to increasing the peak to average ratio yet further. Accordingly, load sharing amplifier suites providing output power levels which are acceptable when such signals are evenly distributed among the amplifiers may overload particular amplifiers when signals are unbalanced as with the above described radiation pattern syntheses.
Although it is possible to avoid the use of such a load sharing amplifier suite, such as by providing a suite of LPAs in the signal paths prior to each input of the beam forming matrix, each such LPA of the suite would be associated with a particular antenna beam signal and, thus, would not provide load sharing. Accordingly, the failure of one such LPA would result in the failure of an antenna beam signal and, thus, would have a substantial affect on the radiation of signals. However, where a matrix arrangement is utilized to feed the amplifiers, if one or even a number of the LPAs malfunction it is still conceivable that performance may be had as signals are distributed among several amplifiers by the input matrix. Accordingly, if a few of the signal components are missing, such as due to failure of one or more of the LPAs, a beam may be formed fairly accurately.
Additionally, it might be possible to avoid the use of the aforementioned load sharing amplifier suite, such as by providing amplification of the signal components provided from the beam forming matrix, i.e., providing LPAs in signal paths directly coupled to each antenna element. However, LPAs are expensive and often cumbersome to implement. For example, they are relatively heavy and therefore often difficult to deploy in a typical antenna system environment. Similarly, the LPAs are active components consuming power and producing heat as a by-product and are susceptible to failure. Therefore, it is generally not desirable to dispose such LPAs in the environment in which the antenna elements and their associated beam forming matrix is disposed.
Therefore, a need exists in the art for a system and method by which various radiation patterns may be synthesized while providing a distributed amplifier arrangement such that signals of particular antenna beams may be provided with amplification via multiple amplifiers without over-driving such amplifiers when synthesizing a radiation pattern co-extensive with multiple ones of the antenna beams. Furthermore there is a need in the art for such systems and methods to allow the disposition of the amplifier suites utilized to be disposed in an environment suitable for their reliable use without causing undesired errors in signals to be combined.